Abstract
[Objective] This study aimed to clarify the difference in the wearing effect of carbon plate built-in shoes (car- bon shoes) depending on the presence or absence of foot functions. [Methods] Healthy adults were classified according to their normal or pronated feet, and their physical char- acteristics, oxygen intake (running economy [RE] value), and pitch number were compared during running in both carbon shoes and non-carbon shoes. [Results] Significant differences in physical characteristics and pitch rate between the two groups were not observed, but the change in RE values with and without the carbon shoes was significantly lower in the pronated foot group than that in the normal foot group. [Conclusion] Carbon plate gain may not be obtained in people with pronated feet because the mobility and function of the ankle joints and feet are different from those of normal feet. Key Words：Borg scale, running movement, Oxygen intake Contact address: Dept. of Physical Therapy, Aomori University of Health and Welfare, 58-1, Oaza-hamadate, aza- mase, Aomori city, Aomori Pref, Japan, +81-17-765-2090, E-mail: t_urushihata@auhw.ac.jp
Journal of International Exercise Sciences Vol.1 No.1 2022 - 41 - Ⅰ．Introduction Carbon shoes are sports shoes for long-dis- tance runners with a carbon plate material em- bedded in the midsole. This shoe has been re- ported to increase propulsion by repulsion of the plate during the takeoff phase and shift the cen- ter of gravity of the body to forward displace- ment 1,2), making it the mainstream shoe for long-distance runners. With this, previous studies have shown that wearing carbon shoes affect oxygen intake 3-6), physical ability such as jumping height and running time 7-9), joint angle, and joint power, with kinematic variables 7-9) as indicators. Among these studies, one study examined the change in oxygen intake when wearing carbon shoes, which includes the running economy (RE) that use oxygen intake as an index when running at a certain speed 7,10-11). In normal shoes, the amount of exercise en- ergy of the lower limb joints generated during the stance phase when running is higher in the ankle joints than that in the hip and knee joints, but the ratio of energy absorption to the amount of exercise energy generated is highest in the toes 9-10). In carbon shoes, focusing on the ineffi- cient characteristics of the toe joint, the rigidity of the carbon plate reduces the braking of the hallux extension angle and the sinking speed of the foot arch in the heel-off phase 3,7,9-11). In the subsequent toe-off phase, it has been confirmed that the mechanical load on the plantar fascia and Achilles tendon is relatively reduced by swinging using the repulsive force due to the elasticity of the plate 11). In fact, a study compar- ing the amount of energy absorbed in the toe joints of normal shoes and carbon shoes re- ported that the heel-off phase was shifted to the toe-off phase with 60%–70% more energy absorption than that of normal shoes 9-10). These reports suggest that the mechanism for improving RE when wearing carbon shoes is to improve the inefficiency of the amount of energy absorbed by the extension of the toe joint through the
shoes and carbon shoes re- ported that the heel-off phase was shifted to the toe-off phase with 60%–70% more energy absorption than that of normal shoes 9-10). These reports suggest that the mechanism for improving RE when wearing carbon shoes is to improve the inefficiency of the amount of energy absorbed by the extension of the toe joint through the rigidity and elasticity of the carbon plate 3,9-10,13). Concurrently, this means that the range of motion (ROM) of the ankles and toes is deeply involved in the improvement of the RE due to the carbon shoes. Conversely, a certain number of healthy peo- ple have a morphology different from that of the foot morphology, called “normal feet” 14). A typi- cal classification of foot morphology includes foot pronation and supination. Of these classifi- cations, foot pronation was confirmed in 46.3% of children 2–6 years of age and in 23% of adults, with a higher relative percentage than foot su- pination 15). These reports indicate that some healthy individuals who use carbon shoes also have a certain percentage of foot pronation and supination. Those with foot pronation and supi- nation are known to have a limited ROM of the ankle and toe joints 16-17), thereby affecting the gait variables 16-18). We hypothesized that people with foot prona- tion and supination, which cause ROM limita- tion in the ankle and toe joints, cannot fully uti- lize the characteristics of the carbon plate, which may affect the RE improvement. If a dif- ference in the RE improvement was observed by wearing carbon shoes due to the difference in foot morphology, it may be applicable to the de- tailed indication criteria of carbon shoes and the presence or absence of indication in people with diseases in the foot. This study aimed to classify foot morphology through qualitative evaluation to determine foot morphology and to compare the RE during running motion by wearing
- 42 - carbon shoes. Ⅱ．Participants and Methods 1．Participants A total of 20 male athletes who lived in the Aomori prefecture and had more than 1 year of experience in medium-distance events of 800 m or 1,000 m and long-distance events of ≥5,000 m (middle distance, 11 people; long distance, 9 people) were included in this study. The recruit- ment of the target population was posted on the bulletin board on campus, and the recruitment was advertised during the track and field com- petition held in the city. Exclusion criteria were those with symptoms of heart disease or corona- virus infection and those with lower limb trauma or disability such as sprains, fractures, or ligament injuries within 6 months. Of the 20 applicants for recruitment, 1 was excluded due to a history of fibula fracture, and the final target was 19 participants (38 legs; age, 18.3 ± 2.5 years; height, 169 ± 5 cm; weight, 58.5 ± 5.6 kg; competition history, 6.6 ± 2.7 years). All participants were given an oral and written ex- planation of the content of this study, and their intention to participate in the study was con- firmed by their signature. This study was ap- proved by the Aomori University of Health Sci- ences Ethics Review Committee (20051). 2. Methods In this study, two types of shoe conditions (carbon and non-carbon conditions) were used. Under carbon conditions, shoes with a carbon plate for the midsole (Zoom Fly 3, Nike Japan Ltd., Tokyo, Japan) were selected. Under non- carbon conditions, shoes using the EVA material Cushlon LT (Zoom Rival Fly 2, Nike Japan Ltd., Tokyo, Japan) were selected for the same part. Both carbon and non-carbon shoes are designed for athletes who can complete 42.195 km within 3 h and 30 min to 4 h according to the manufac- turer’s official chart 20). The RE was measured using the oxygen in- take (mL/min) during running on a self-pro- pelled treadmill (Autorunner AR-200, Minato Medical Science Co., Ltd., Osaka, Japan) as an index. A respiratory metabolometer (AE310S, Minato Medical Science Co., Ltd., Osaka, Ja- pan) was used to
3 h and 30 min to 4 h according to the manufac- turer’s official chart 20). The RE was measured using the oxygen in- take (mL/min) during running on a self-pro- pelled treadmill (Autorunner AR-200, Minato Medical Science Co., Ltd., Osaka, Japan) as an index. A respiratory metabolometer (AE310S, Minato Medical Science Co., Ltd., Osaka, Ja- pan) was used to measure the oxygen intake. The experimental protocol was to have the par- ticipants rest for 2 min while sitting on a chair during the treadmill exercise and then warm up for 5 min at a running speed of 2.5 m/s. Subse- quently, to eliminate the influence of the wear- ing order, shoes under the carbon or non-carbon condition selected in random were worn, and the running speed was 3.33 m/s for 5 min. There were a total of four trials, with two trials each for the carbon and non-carbon conditions. In this study, for the effective function of the shoes used, a running speed of 3.33 m/ was selected from the time the experiment ended as an- nounced by the developer 19). At the end of each trial, the Borg index was calculated, which cor- responds to subjective fatigue in a standing po- sition on a 15-point scale 19). In consideration of the physical fatigue experienced by the partici- pant during the trial, a 5-min rest was provided for each participant while sitting in a chair. In addition, the same socks were used when wear- ing the shoes. To measure the RE in this study, the partici- pants were instructed not to speak after the start of the experiment and to note the ratio of exhalation to inspiration (1:1). To clarify the change in shoe conditions due to the difference in foot morphology, the amount of change in the
Journal of International Exercise Sciences Vol.1 No.1 2022 - 43 - RE value and pitch number (carbon condition minus non-carbon condition) was calculated and used as the measured value. Data analysis targeted the latter 2 min of transition to the steady state as the oxygen in- take was recorded continuously every 5 s under the carbon and non-carbon conditions. The measured RE value was obtained by extracting and averaging the oxygen intake every 15 s di- vided by the body weight (mL/kg/min). In this study, the number of pitches during driving was also measured. To measure the number of pitches, a video camera was installed on the sagittal plane of the treadmill (height 0.45 m, distance 1.25 m). For the number of pitches in each trial, the number of steps in the latter 2 min was visually counted from the video, and the average number of pitches (steps) in the two trials was used as the measured value. Foot morphology was determined using the Foot Posture Index-6 (FPI-6) 21), which is an in- dex to qualitatively evaluate the foot morphol- ogy of the participant. For each item, palpation of the talus head, observation of the curve above and below the lateral malleolus, observation of the calcaneal varus and valgus position, obser- vation of the bulge of the calcaneal joint, obser- vation of the medial longitudinal arch, and ob- servation of the medial–lateral dislocation of the forefoot with respect to the hindfoot were carried out. It consists of a total of six items and is judged in five grades from −2 to +2. Pronation or supination of the foot is classified when the participant obtains ≥6 points or <−1 point, and normal foot, if otherwise 22). In this study, the to- tal FPI-6 points of the left and right feet were classified to clarify the effects of foot morphology. At the time of measurement, to minimize the er- ror of variation among evaluators, the FPI-6 was scored, and the markers were placed by the same inspector. Of the 19 participants, through the FPI-6, 4 were classified with foot pronation or supination
tal FPI-6 points of the left and right feet were classified to clarify the effects of foot morphology. At the time of measurement, to minimize the er- ror of variation among evaluators, the FPI-6 was scored, and the markers were placed by the same inspector. Of the 19 participants, through the FPI-6, 4 were classified with foot pronation or supination (pronated foot group), and 16 were classified with normal feet (normal foot group). The participants’ basic characteristics were obtained, such as age, height, weight, competi- tion history, ROM of the ankle joint, lower limb length (trochanteric fruit length, spine fruit length), foot length, foot circumference, and foot width. The ROM of the ankle joint was meas- ured using a joint goniometer (University of To- kyo goniometer, Matsuyoshi & Co., Ltd., Tokyo, Japan). According to the measurement method of the Japanese Society of Orthopedic Surgery and the Japanese Society of Rehabilitation Medicine, the ROM in the direction of dorsiflex- ion, plantar flexion, supination, and pronation of the ankle joint was measured in 1° incre- ments. The measured value was the average value (°) on the left and right sides in each di- rection of motion. The length of the lower limbs was measured in the supine position using a tape measure. The trochanteric fruit length was recorded from the upper edge of the greater trochanter to the lower end of the lateral malleolus, and the spine length was recorded as the linear distance from the most protruding part of the anterior superior iliac spine to the lower end of the me- dial malleolus in 0.5-cm increments. The meas- ured values were the average values (cm) on the left and right sides of the trochanteric fruit length and spine fruit length. The foot length, foot width, and foot circumference were meas- ured in a static standing position using a tape measure in the same manner as that in the lower limb length. The foot length is the straight distance from the midpoint of the
foot length, foot width, and foot circumference were meas- ured in a static standing position using a tape measure in the same manner as that in the lower limb length. The foot length is the straight distance from the midpoint of the
- 44 - lateral diameter of the heel to the tip of the sec- ond toe, the foot width is the straight distance from the medial aspect of the first metatarsoph- alangeal joint to the lateral surface of the fifth metatarsophalangeal joint, and the foot circum- ference is the measurement point of the foot width. The circumferences of each of the afore- mentioned were recorded in units of 0.1 cm. The measured values of foot length, foot width, and foot circumference were all average values (cm) on the left and right sides. SPSS (version 24, IBM Japan, Ltd., Tokyo, Ja- pan) was used for statistical analysis. To com- pare the Borg index and RE values caused by different shoe conditions, a paired t-test was se- lected after confirmation of normality. The Mann–Whitney U test was performed to com- pare the physical characteristics due to the dif- ference in foot morphology and the amount of change in the RE value and pitch number. The significance level was set to 5%. Ⅲ. Results Table 1 shows the mean and standard devia- tion of the Borg scale and RE values under car- bon and non-carbon conditions. Paired t-test re- sults showed no significant difference in the Borg scale scores between the two shoe condi- tions. In contrast, the RE value was signifi- cantly lower in the carbon condition than that in the non-carbon condition. Table 2 shows the average value and standard deviation of the physical characteristics due to the differences in foot morphology. As a result of the Mann–Whitney U test, no significant differ- ence was observed in any of the items, except for the FPI-6 total score and foot width, between the two groups. Table 3 shows the average value and standard deviation of the changes in the RE value and the number of pitches due to the differences in foot morphology. As a result of the Mann–Whitney U test, the amount of change in the RE value in the pronated foot group was significantly smaller than that in the normal foot group (nor- mal foot group and pronated foot group,
standard deviation of the changes in the RE value and the number of pitches due to the differences in foot morphology. As a result of the Mann–Whitney U test, the amount of change in the RE value in the pronated foot group was significantly smaller than that in the normal foot group (nor- mal foot group and pronated foot group, carbon condition, 39.1 ± 3.4 and 41.5 ± 4.4 mL/kg/min; non-carbon condition, 39.9 ± 3.8 and 41.4 ± 4.3 mL/kg/min, respectively). No significant differ- ence was found in the amount of change in the number of pitches due to the difference in foot morphology (normal foot group and pronated foot group, carbon condition, 338.4 ± 19.2 and 350.8 ± 19.3 steps; non-carbon condition, 339.1 ± 17.4 and 351.3 ± 18.3 steps, respectively). IV. Discussion This study aimed to compare the RE values of wearing carbon shoes on a treadmill running at a speed of approximately 12 km/h (3.33 m/s). As a result, carbon shoes significantly reduced the average oxygen intake after the steady state compared to that of the control shoes. Table 1. Comparison of RE value between carbon and non-carbon conditions Items Units Carbon condition Non-carbon condition Mean SD Mean SD Borg scale Points 10.5 2.6 10.5 2.5 Average RE value* mL・kg -1 ・min -1 39.6 3.7 40.2 3.8 RE, running economy. * p < 0.05
Journal of International Exercise Sciences Vol.1 No.1 2022 - 45 - The improvement rate of the RE value in this study was 1.5% higher by wearing carbon shoes than that of normal shoes. This improvement rate saves approximately 2.9 m of energy per minute when converted to running distance us- ing the regression equation of the previous re- search 23). Similarly, several studies have been reported that verified the change in the RE value due to the use of carbon shoes while run- ning on a treadmill. Hunter et al. 5) reported that a 1.9% improvement was observed in the RE value of carbon and non-carbon shoes when run- ning on a treadmill at 16 km/h for male mara- thon athletes. In addition, in a study that Table 2. Comparison of the participants’ basic characteristics between the normal and pronated foot groups Items Units Normal foot group (n=15) Pronated foot group (n=4) Mean SD Mean SD Age Years 18.1 2.6 18.8 3.1 Height cm 167.9 4.4 173.3 6.2 Weight kg 57.7 4.7 61.5 8.7 Competitive career Years 6.8 2.5 5.9 3.8 FPI-6 score** Points 2.3 1.9 8.0 1.4 Dorsiflexion ROM Degree 23.8 8.1 26.5 3.1 Plantarflexion ROM Degree 44.5 6.4 46.5 5.4 Eversion ROM Degree 16.5 5.4 15.8 1.5 Inversion ROM Degree 32.3 8.2 38.0 8.1 SMD cm 85.9 2.9 86.5 4.5 TMD cm 78.3 2.8 79.3 6.5 Foot length cm 25.5 1.1 26.0 1.4 Foot width* cm 9.5 0.6 10.5 0.6 Foot circumstance cm 23.3 1.0 24.5 1.0 FPI-6, Foot Posture Index-6; ROM, range of motion; SMD, spinomalleolus distance; TMD, trochantomalleolus distance. * p < 0.05, ** p < 0.01 Table 3. Comparison of running variables and change value of the RE between the normal and pronated foot groups Items Units Normal foot group (n=15) Pronated foot group (n=4) Mean SD Mean SD Change value of RE* mL・kg -1 ・min -1 −0.8 1.1 0.1 0.2 Change value of pitch rate Steps −2.9 2.5 −2.2 2.3 RE, running economy. * p < 0.05
Items Units Normal foot group (n=15) Pronated foot group (n=4) Mean SD Mean SD Change value of RE* mL・kg -1 ・min -1 −0.8 1.1 0.1 0.2 Change value of pitch rate Steps −2.9 2.5 −2.2 2.3 RE, running economy. * p < 0.05
Description
The study compares running economy in athletes with normal and pronated feet using carbon shoes.